The present invention relates to a system for accurately positioning blocks of digital data on a magnetic medium so that these blocks can be rewritten successive times without interferring with adjacent blocks, the recording method employed being phase encoding on a single track containing both the data and the format information.
In recording digital data on a moving magnetic medium such as a tape, disc, drum or the like, it is often necessary to re-record blocks or segments of the medium without interferring with adjacent blocks. This is accomplished by accurately positioning the block on the medium by reading a previously recorded timing or format track during the write or record operation. In those systems wherein a single track is employed for the data and the format information, the format is read to ascertain that the correct block is adjacent thereto. The system then shifts into the write mode and data is written in the block. Thus, the newly written block and the previously written format information adjacent thereto have been written at different times. In systems wherein the phase encoding method is employed, the data and the format information can therefore be out of phase. When the system is in the read mode, the phase encoder will properly set up following the interrecord gap and will correctly read the block marker. However, if the stored data adjacent to the block marker is out of phase therewith, that data cannot be detected by the phase decoder. Thus, in systems employing the phase encoding method of recording, wherein data was stored on one track, a separate track was required for the format information.